1. Field of the Invention
The present invention relates to an optical information recording and/or reproducing apparatus for optically recording or reproducing information by relatively translating an optical head to an optical information recording medium so as to scan information tracks in the recording medium with a light beam from the optical head. More particularly, the invention relates to an optical information recording and/or reproducing apparatus using a vibration wave driving device as means for moving the optical information recording medium and a vibration wave motor device capable of providing an output characteristic precisely irrespective of environmental changes.
2. Related Background Art
Recently, optical information recording and/or reproducing apparatus for optically recording or reproducing information with a light beam are drawing attention among information recording and/or reproducing apparatuses for recording or reproducing information on a recording medium. As the recording medium for optically recording or reproducing information there are those of a disk type, a card type, etc., among which card type recording media (hereinafter referred to as optical cards) are excellent in productivity, portability and accessibility and have a wide range of applications.
Information is recorded in the recording medium by scanning information tracks with a light beam of a fine spot modulated according to recording information, and is recorded in the form of information bit strings optically detectable.
On the other hand, information is reproduced from the recording medium by scanning the information bit strings on the information tracks with a light beam spot of constant power not enough to result in recording in the medium and then detecting reflected light or transmitted light from the recording medium.
The optical head used in recording or reproducing the information in or from the above recording medium is relatively movable with respect to the recording medium in directions along the information tracks and in directions traversing the information track directions, and movement of the optical head causes the light beam spot to scan the information tracks.
The optical head is provided with a converging lens for converging the light beam spot, an example of which is an objective lens. The objective lens is held so that it can move independently with respect to the optical head body in directions along the optical axis thereof (or in focusing directions) and in directions perpendicular to both the directions along the optical axis and the directions of the information tracks on the recording medium (or in tracking directions). Such holding of the objective lens is generally effected through an elastic member, and the movement of the objective lens in the two ways described above is generally driven by an actuator utilizing magnetic interaction.
FIG. 1 is a diagrammatic, plan view of a write-once optical card. There are a lot of information tracks 1001 arranged on an information recording surface of optical card 1000 in parallel in L-F directions. Also, a home position 1002 is provided as a reference position of access to the information tracks 1001 in the information recording surface of optical card 1000. The information tracks 1001 are arranged in the order of 1001-1, 1001-2, 1001-3, . . . from the side of home position 1002. Further, as shown in FIG. 2, there are tracking tracks 1003-1, 1003-2, 1003-3, . . . provided adjacent to the corresponding information tracks. These tracking tracks are used as a guide for autotracking (hereinafter referred to as AT) for controlling the beam spot so as not to depart from a selected information track during the scanning with the light beam spot in recording or reproducing information.
This AT control is performed using a servo system in the optical head, which is arranged so that deviation (AT error) of the above light beam spot from an information track is detected and this detected information is negatively fed back to a tracking actuator for driving the objective lens described above in the tracking directions, whereby the light beam spot is let to follow the desired information track while moving the objective lens relative to the optical head body in the tracking directions (along the D direction).
The AT control uses light spots of S.sub.1 and S.sub.3 and utilizes reflected light from tracking tracks on which the light spots S.sub.1, S.sub.3 impinge. Recording and/or reproduction of information is carried out using a light spot S.sub.2 located between the two light spots S.sub.1 and S.sub.3 The light spots S.sub.1, S.sub.2, S.sub.3 are obtained from a same light source so that they are formed at equal intervals with the light spot S.sub.2 between the light spots S.sub.1 and S.sub.3 by interference effect of a diffraction grating located between the light source and the objective lens.
While the information tracks are scanned with the light beam spot upon recording or reproducing information, autofocusing (hereinafter referred to as AF) control for the objective lens is carried out in order to shape (or focus) the light beam in a spot of an appropriate size on a recording surface of the optical card.
This AF control is carried out in such a manner that deviation (AF error) of the above light beam spot from an in-focus state is detected in the optical head, the thus detected signal is negatively fed back to a focusing actuator for moving the objective lens along the optical axis thereof, and the objective lens is moved relative to the optical head body in the focusing direction to focus the light beam spot on a recording surface of the optical card.
Meanwhile, as a method for relative scan between the light beam emitted from a semiconductor laser and the optical card, the optical card is mounted on a base (hereinafter referred to as a carriage), which is not movable in the directions along the tracks in the optical card but movable in the directions traversing the track directions, and the optical head body is moved using a voice coil motor in the directions parallel to the tracks on the optical card.
A vibration wave driving device (for example, an ultrasonic motor) is used for moving the carriage.
A first reason why the carriage is arranged to move in the directions perpendicular to (or traversing) the information tracks in the optical information recording and/or reproducing apparatus in the above structure is to enable access to another information track, and in this case, high-speed scanning is conducted in conventional apparatus while keeping the AT control in an off state.
A second reason is as follows. If there is deviation (hereinafter referred to as skew) as to parallelism between the tracks on the optical card and the scanning system in the track directions, for example in the case where the optical card is not regularly mounted on the carriage, and when the scanning in the track directions is performed while keeping the AT control in an on state, the objective lens is drive-controlled so as to be biased relative to the optical head body. There is, however, a limit in a biasing amount of the objective lens relative to the optical head body. Thus, the biasing amount could reach the limit during scanning in the length direction of the track. Therefore, the second reason is to keep the bias of the objective lens relative to the optical head body within a permissible range by moving (or relatively and finely moving) the carriage in the directions perpendicular to the tracks during scanning of light beam.
Here is briefly described the structure and the principle of driving of the vibration wave driving device.
A vibrator is formed by bonding a piezoelectric device which is an electricity-mechanical energy conversion element with an adhesive or the like to an elastic body made of a low-vibration-damping metal, for example an elastic body formed in an elongate oval shape, the vibrator is fixed to the back face or side surface of the carriage as described previously on the piezoelectric device side, and a straight portion on one side of a free end face of the elastic body is brought into press contact through a pressing means with a rail stator extending along the moving direction of the carriage.
The piezoelectric device includes piezoelectric device groups of two phases A and B separated at an odd multiple of a quarter wave from each other, and in each group there are formed piezoelectric devices different in polarizing-treatment direction in the thickness direction at intervals of .lambda./2. Then cyclic voltages such as alternating voltages with a phase difference of 90.degree. therebetween are applied to the piezoelectric device groups of the two phases A, B, whereby standing waves are oscillated by the respective piezoelectric device groups of the two phases A, B. The standing waves are synthesized to form traveling waves, which cause surface particles in the free end face of the elastic body to make an elliptical motion in a plane along the thickness direction, thereby moving the carriage by frictional drive against the stator.
FIGS. 3A to 3E are signal diagrams to show the operation of the above conventional example. FIG. 3A shows output signals from a lens position detecting circuit for detecting the position of the objective lens where the carriage with the optical card mounted thereon is moved by a short distance in the direction perpendicular to the tracks in an on state of tracking when the lens is located at distance m to the center position of lens. In this case, because the AT control is on, a motion of the objective lens relative to the optical head body becomes nearly equal to a motion of the carriage relative to the optical head body.
The vibration wave driving device starts moving the carriage at time t.sub.1 in the direction perpendicular to the tracks.
FIG. 3B shows an on-off signal of the vibration wave driving device, which is on in a time period between time t.sub.1 and time t.sub.4.
FIG. 3C is a drive voltage of the vibration wave driving device. The voltage is constant between time t.sub.1 and time t.sub.3 and the drive voltage is gradually decreased between time t.sub.3 and time t.sub.4 so as to decelerate to stop the carriage.
When the drive voltage of the vibration wave driving device is constant, the drive frequency determines a drive speed of the vibration wave driving device, that is, a velocity of the carriage (hereafter referred to as a carriage velocity) in the direction perpendicular to the tracks with respect to the optical head body. Here, FIG. 4 shows a relation of the carriage velocity v against the drive frequency f of the vibration wave driving device.
Let a state A (a curved solid line) represent a state in which the carriage velocity is V.sub.OA when the drive frequency of the vibration wave driving device is f.sub.0, as shown in FIG. 4. In FIG. 3A, the carriage starts moving at time t.sub.1, then the carriage velocity becomes approximately constant after the delay time t.sub.2, the carriage starts decelerating at time t.sub.3, and it stops at time t.sub.4. In this case, a moving distance of the objective lens relative to the optical head is m-n.sub.1.
Further, FIG. 3E shows the moving velocity of the objective lens and at the same time, indicates that the carriage velocity is approximately constant between time t.sub.2 and time t.sub.3.
FIG. 3D indicates the position of the light beam relative to the track (AT error) when the above carriage movement was performed. In FIG. 3D the solid line shows a change of AT error corresponding to the changes of the solid lines shown in FIG. 3A and FIG. 3E. As seen from FIG. 3D, the AT error becomes temporarily large upon the movement start of the carriage and again becomes large upon deceleration.
FIG. 5 is a structural drawing to show an example of the optical card recording and/or reproducing apparatus for recording or reproducing information in or from the optical card. In FIG. 5, reference numeral 200 designates the optical card being an information recording medium, and 201 the carriage on which the optical card 200 is mounted. The carriage 201 is arranged to be movable in the directions traversing the information tracks by drive of the vibration wave driving device (composed of a vibrator 202 and a carriage drive circuit). Numeral 202 denotes the vibrator. Numeral 203 represents the optical head in which a semiconductor laser as a light source and a photoelectric transducer are incorporated, 204 the objective lens provided on the optical head 203 to converge a light beam and to irradiate the optical card 200 therewith, 205 a comparator for comparing an information track intersecting signal output from the optical head 203 and inputting a result to MPU 206, 206 MPU for controlling the elements in the apparatus, 207 a carriage drive circuit for controlling the drive of vibrator 202 under a command from MPU 206, and 208 a lens position detecting circuit for outputting a deviation amount of objective lens 204 from the center position of optical head 203, output from the optical head 203, to MPU 206. Numeral 209 denotes a memory device for storing the voltage output to the carriage driving circuit 207 and the moving velocity of the carriage 201.
Here, suppose the light beam output from the optical head 203 is located on a certain information track on the optical card 200. A so-called seek control is performed in this case to move the light beam to another information track. If a target information track is outside a movable range of the objective lens 204 in the optical head 203, MPU 206 outputs a command to drive the vibrator 202 to the carriage driving circuit 207. The carriage driving circuit 207 outputs a drive voltage with a drive frequency and an amplitude preliminarily set in MPU 206 to the vibrator 202, thereby driving the carriage 201 with the optical card 200 mounted thereon. This relatively moves the information tracks on the optical card 200 in the information-track-traversing direction with respect to the light beam output through the objective lens 204, so that the optical head 203 outputs an information track intersecting signal through the comparator 205 to MPU 206 every time the light beam traverses an information track. When a number of input pulses from the comparator 205 reaches a target value, MPU 206 then outputs a command to stop the drive of vibrator 202 to the carriage driving circuit 207. Then the carriage driving circuit 207 stops the output of drive voltage so as to stop the carriage, thus completing movement of the light beam to the target information track.
Relative fine movement is next described. Suppose the optical card 200 has a skew angle .theta. as shown in FIG. 6. Let us consider a case that the objective lens 204 was moved relative to the optical head 203 to a left or right limit in the movable range from the center while the optical head 203 was kept in a scanning operation on an information track in an autotracking state. Since a current position of the objective lens 204 is input from the optical head 203 through the lens position detecting circuit 208 to MPU 206, MPU 206 judges from this signal that the objective lens is at the movable limit and gives the carriage drive circuit 207 such a command that the carriage drive circuit 207 should output to the vibrator 202 a drive voltage with such a drive frequency and an amplitude as to keep the moving velocity of carriage 201 slower than that in the seek control preliminarily set, thereby moving the carriage 201 so that the objective lens 204 is brought to the center of optical head 203. As soon as the information tracks on the optical card 200 start moving, the objective lens 204 also starts moving in the same direction because it is in the autotracking state. Since the position of objective lens 204 is input through the lens position detecting circuit 208 to MPU 206, a command to stop the output of drive voltage to the vibrator 202 is sent to the carriage drive circuit 207 when the objective lens 204 reaches the center position of optical head 203.
In this manner, correction is made in movement of the light beam to the information track and in positional relation between the light beam and the information track.
The relation between the drive frequency of the vibration wave driving device and the carriage velocity, however, is not constant because of machine differences, changes in environmental conditions such as the temperature or the humidity, changes with time, etc. Therefore, a same velocity would not be achieved even if drive is made at a constant drive frequency and a constant drive voltage.
The optical information recording and/or reproducing apparatus had such a problem that in the case of fine feed to move the carriage with the optical card mounted thereon in the direction perpendicular to the tracks in the tracking state with the AT control being on, for example if the moving speed of the carriage increases so as to make an AT error exceed a permissible value upon movement of carriage, the light beam deviates from a track to become incapable of recording or reproducing information, in turn causing track off.
Conversely, if the moving velocity of the carriage is too low, a moving amount per unit time becomes small, thereby failing to achieve a necessary moving amount.
Here, the state B shown by the dashed lines in FIGS. 3A-3E represents a case that the moving velocity of the carriage became higher in spite of the same drive frequency. FIG. 4 shows a case that the relation between the drive frequency (f) of the vibration wave driving device versus the velocity (v) changed from the state A to the state B because of machine differences, environmental conditions, changes with time, etc. Suppose the change is from the state A represented by the solid line on which the velocity v.sub.OA was attained by drive frequency f.sub.0 to the state B represented by the dashed line B on which the velocity v.sub.OB is obtained by drive frequency f.sub.0. When the vibration wave driving device is driven at the same drive frequency f.sub.0, the carriage starts moving at time t.sub.1 as in the state B shown by the dashed lines in FIGS. 3A-3E, the velocity becomes greater than that in the state A shown by the solid line, and the carriage starts decelerating at time t.sub.3 then to stop at a position of n.sub.2 at time t.sub.4. In this case, because the device is decelerated and stopped from the large velocity, the AT error becomes greater as shown in the state B represented by the dashed line in FIG. 3D as against that in the state A shown by the solid line. Therefore, there was a drawback that the deviation of the light beam relative to the track became greater, thereby making normal recording or reproduction impossible.
Since the seek operation requires a higher speed than in the fine feed operation of carriage, the carriage is driven at drive frequency f.sub.1 in the state A shown by the solid line in FIG. 4, thereby achieving a desired carriage velocity v.sub.1A. However, if the relation of drive frequency versus carriage velocity changes as shown in the state C shown by the chain line, the carriage velocity at drive frequency f.sub.1 is just v.sub.1C, thus failing to obtain a desired velocity. Therefore, there was a drawback that the necessary time for seek operation became longer.